When hydrogen will contribute to climate change and when it won’t.

Hydrogen is often touted as a climate hero because when used as a fuel in things like buses or steel production, there are no direct carbon emissions (or associated warming ) to fear. As the world tries to reduce our consumption of fossil fuels, there could be many new demands for this carbon-free source of energy.

But how hydrogen is made could determine how useful it is for the climate. This is where the rainbow comes in. (I’ve added a summary chart below so you can sort out all these colors.)

Last week, the European Commission published rules that define what “renewable” hydrogen is: in other words, what it means for hydrogen to be Green. There was also a fascinating story in Science last week about the natural occurrence, or goldhydrogen.

So let’s dive into the hydrogen rainbow and explore where this fuel of the future could come from.

Why do we need hydrogen?

We already use a lot of hydrogen today: global demand was 94 million metric tons (Mt) in 2021. Most of it was used for oil refining, as well as ammonia production (for fertilizer) and methanol (for the manufacture of chemicals).

This is likely to change in the future, as it is also a good replacement for fossil fuels in transport, heavy industry and other sectors. If countries meet their climate commitments, hydrogen demand could reach 130 Mt by 2030, around a quarter of which will be for new uses.

The problem is that hydrogen production today massively requires fossil fuels, usually natural gas. In so-called “grey” hydrogen production, natural gas reacts with water, generating hydrogen gas and releasing carbon emissions.

It doesn’t have to be that way, though. On the one hand, we could try to capture carbon emissions from the production of hydrogen from fossil fuels (this method produces so-called blue hydrogen). This is quite a controversial approach, as carbon capture is expensive and doesn’t always work efficiently.